Jeffrey,
Certainly Nortel in the 1990s and BlackBerry (2001-2015) saw no need to
clean no-cleans.

Nortel:
Products had to last in the field for up to 25 years, with no cross talk.
Every stinking chemical that came in contact with a printed circuit pack was
tested by halide ion spot test, copper mirror, SIR and electrochemical
migration.  The latter two tests were to Bellcore spec, NOT just E8 ohms.
Non-liquid chemicals were applied to SIR/ECM boards with a  50:50
IPA:toluene mix as many tested using just IPA would pass.  Failure rate of
materials during chemical qualification was high.
Most components were PTH or leaded.  BGAs were 1 mm pitch or more, so
stand-off was excellent and fluxes got properly "cooked".  Excellent process
controlled helped.
Almost never conformal coating.

BlackBerry:
Products life was 2 years.
Every stinking chemical that came in contact with a printed circuit pack was
tested by halide ion spot test, copper mirror, SIR and electrochemical
migration.  SIR testing to E8 ohms was good enough.  Failure rate of
materials during chemical qualification was about 30%. Used Nortel's
IPA/toluene mix.
Component mix was one PTH (a connector); the rest SOICs, etc.; chips down to
0402s, BGAs to 0.4 mm pitch and there were QFNs. 
Excellent process control helped.
Never conformal coating.

Regards,
Bev


-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Jenkins, Jeffrey (US)
Sent: Thursday, February 27, 2020 3:11 PM
To: [log in to unmask]
Subject: [TN] No-Clean (ROL0) question....

Fellow TechNetters,

I apologize if this may seem like a newbie question and if so I apologize.
I've used OR fluxes and RO fluxes and have always had them removed by the
cleaning process as most of the products that I work on have an expected
life of 10+ years.  We've typically validated the amount of WOA and
Chlorides and set baselines for those.

Someone posed me a question about cleaning no-cleans. Even though in a
perfect world a no-clean flux should be 100% inactive after reflow, I'm
betting that's never perfectly the case.   So my view and response was that
based on the life span and end use environment, my concern would be
humidity/moisture mixing with the residual material and in the long term
increasing the risk of dendritic growth and other things.  Am I off the
mark?

Thanks,

Jeffrey A. Jenkins, CID+
Principal Engineering Designer
Cubic Mission Solutions

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